Work machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump on the work machine that provides pressurized liquid to chambers within the actuators. As the pressurized liquid moves into or through the chambers, the pressure of the liquid acts on hydraulic surfaces of the chambers to effect movement of the actuator. When the pressurized liquid is drained from the chambers it is returned to a low pressure sump on the work machine.
One problem associated with this type of hydraulic arrangement involves efficiency. In particular, the liquid draining from the actuator chambers to the sump has a pressure greater than the pressure of the fluid already within the sump. As a result, the higher pressure fluid draining into the sump still contains some energy that is wasted upon entering the low pressure sump. This wasted energy reduces the efficiency of the associated hydraulic system.
One method of improving the efficiency of such a hydraulic system is described in U.S. Pat. No. 6,480,781 (the '781 patent) issued to Hafner et al. on Nov. 12, 2002. The '781 patent describes a fuel system having a plurality of fuel injectors that are hydraulically actuated by way of high pressure engine oil. The fuel system includes a means for recovering hydraulic energy from oil leaving each of the fuel injectors. The means for recovering hydraulic energy includes a waste accumulating fluid control valve for each injector, and a hydraulic motor connected between a high pressure pump and the waste accumulating fluid control valves. As the actuating oil exits each fuel injector, it enters and drives the motor before being divided into two separate flows. A first of the two flows is directed to the high pressure pump, while the second is returned to an actuation fluid sump.
Although the means for recovering hydraulic energy described in the '781 patent may improve efficiency of the associated fuel system by driving the motor and associated pump with waste oil, it may be limited and problematic. In particular, because the means for recovering does not provide a way to store recovered energy, it may still be wasted if the demand for recovered energy is not immediate. In addition, because the pressure of the fluid exiting the fuel injectors may fluctuate significantly depending on injector operation, and because the means for recovering is directly associated with the high pressure pump, operation of the high pressure pump may also fluctuate significantly. This fluctuation of the high pressure pump could affect injector variability causing engine instability. Further, because oil from the motor may be diverted directly to the high pressure pump, air entrained within the oil may remain in the oil, causing sponginess in the hydraulic circuit.
The disclosed hydraulic system is directed to overcoming one or more of the problems set forth above.